Furnace grate



F. GRAAFEN FURNACE GRATE Oct. 2, 1934.

Filed July 27, 1932 IN ENTOR %1 ATTORNEY Patented Oct. 2, 1934 FURNACE GRATE r Ferdinand Graafen, Zwickau, Germany Application July 27, 1932, Serial No. 624,947

In Germany August 10, 1929 8 Claims.

My invention relates to improvements in furnace grates.

According to the present invention, the grate is built up of longitudinally extending grate members, some or all of which have reciprocating movements imparted thereto for feeding the fuel along the grate, and are subjected to a direct or indirect cooling. g

The invention is especially well suited to mechanically stoked furnace grates.

It has already beensuggested to feed or advance the fuel on a grate surface by building the grate of individual members or fire bars extending longitudinally of the grate, the individual feed members being moved longitudinally to-andfro relative to one another.

This reciprocating movement can be carried out in a number of ways. All the members of the grate can be moved, or only some of them, for example, one-half or two-thirds of all the members of the grate. The movement can be such that the fire bars, or members, are moved to-and-fro alternately relative to one another, Or, some of the bars, for example, every third bar, can be moved forward a predetermined distance towards the inlet end of the furnace, and then another like series of bars, moved forward, and so on, after which all the bars are moved back together to thebridge, or towards the inner end of the furnace. Combined with the-above movements, or in the case of any'other movement, the bars, or members, can be lowered somewhat below the plane of the grate, and return thereto on the return movement. Or, the upper side of some, or of all the fire-bars or members, may be provided with teeth or projections, the steep flank of the tooth being towards the bridge or inner end of the grate so as to facilitate thefeed of the fuel. 1 V

There is a risk in these and similar grates, of the grate members which inmany cases areof substantial length, burning out, or becoming warped by overheating, thus setting up jamming between the'moving parts and interrupting the proper working of the grate, or-putting it entirely out of action.

An object of the present invention is to overcome this disadvantage and to permit the employment of grates of this kind, regardlessof their width and length, by the cooling of the members of the grate by means of a suitable cooling medium.

A particularly suitable and advantageous form of construction of furnace grate according to this inventionis one in which the grate members which carry the fuel are'cooled indirectly, that is to say, are cooled by tubes, through which the cooling medium flows, located adjacent to and alongside the grate members and also extending in a longitudinal direction. In such construction none of the grate members, or at least not those which execute a to-and-fro movement for the purpose of feeding the fuel, need to be provided with inlets and outlets for the cooling medium, so that a grateof a simplified design and consequently less expensive to build is made possible. The application of cooling to. the grate members which extend in the longitudinal direction of the grate and are moved to-and-fro in that direction for the purpose of feeding the fuel, provides a very efficient grate of this type since overheating of the grate members, or fire-bars, with all its accompanying disadvantages is over-- come.

:Any suitable cooling medium, such as water, may be used for cooling the grate members. The cooling tubes extending in the longitudinal direction of the grate, may be of such a nature, as to obtain a thermo-siphon like automatic circulation of the cooling water when the grate is slight- 1y inclined. More particularly, it is possible to connect the tubes charged with the cooling liquid to the boiler vessel itself. In the case of watertube boilers, the tubes may form the down-comers for conducting the water from the upper, or steam, drum to the lower, or mud, drum. I Or, an independent-supply of cooling water, or any other suitable medium, may be circulated through the cooling tubes and passed into cooling apparatus for abstraction of some of its heat. The recovered heat may be utilized for the preheating of the air supply, or for'other suitable purposes.

On the accompanying drawing illustrating by way of example various'embodiments of furnace grates according to the present invention,

Fig. 1 is a sectional'view of a grate construction in which, intermediate the directly cooled members of thegrate, are members which are cooled indirectly by the adjacent directly cooled members.

Figs. 2 and 3 are similar sectional views of other grate constructions and Fig. 4 is a fragmentary side view of a portion of a grate of the Fig. 2 form showing conventional means for solely reciprocating the reciprocal grate members.

It is to be understood that the number of grate members making up a grate is dependent upon the width of the grate.

According to Figs. 1-3, the grate is composed of internally cooled tubes 0, between which are provided feeders b which are only cooled by radiation or reflection of the surplus heat on to the adjacent cooled tubes. This indirect cooling by means of adjacent cooled tubes forms a part of the present invention. Although in the case of all the'grate constructions illustrated in Figs. 1, 2 and 3 the necessary air gaps in the grate are arranged between the internally-cooled tubes 0 and the feeders b, the indirect cooling of the latter is quite suihcient to prevent any burning out Or warping thereof, The main advantage of the grate construction hereinafter described is that it is not necessary to directly cool the feeders which when moved effect the feed of the fuel, as the indirect cooling is amply sufficient. Thus, for example in the grate constructions shown in Figs. 1, 2 and 3 the cooling tubes 0 are stationary, and the feed of the fuel is effected by the moving of the feeders b in any suitable phase of movement. If desired, the feeders b, and in some cases the tubes 0,. may be provided with teeth, or projections 2.

Fig. 1 shows stationary tubes of triangular cross section. Fig. 2 shows tubes of circular cross section with fiat plates 11 welded thereto, while Fig. 3- shows rectangular tubes which on their lower side are provided with a flange-like projection q that can be utilized for mounting these tubes in suitably shaped dove-tailed carriers. Ordinary round tubes can of course also be used.

While it has already been stated that these grate constructions are particularly suitable, because only the'feeders, which have no coolingmedium connections, are moved, it is to be understood that grate constructions are included in the present invention in which the indirectly-cooled members are stationary and the cooling tubes are moved. With such constructions the main advantages of the invention would be realized, that is to say, the individual members of the grate which extend in a longitudinal direction are cooled either directly or indirectly, with a view to avoiding any burning out, or warping, of the members due to overheating.

Air-gaps are provided between the grate members in the usual way.

From the foregoing description it will be seen that an automatic feed-grate or mechanical stoker has been produced of economical manufacture construction and favourable to manufacturing. These advantages are due to the fact that the principle of indirect cooling has been applied according to the present invention to grates in which the feed of the fuel is effected by the moving of the individual members of the grate to-and-fro in any desired manner in the longitudinal direction of the grate.

It has already been pointed out that the grate may be an inclined grate, in which the rearward end, is lower than the front end, whereby the feed of the fuel is facilitated, more especially so where none of the members of the grate or only some of them are provided with teeth or projections and Where only some of the members of the grate are given a to-and-fro motion in any desired phase.

By the system of cooling herein adopted, the new grate is also particularly suitable for high efiiciency and radiant boilers in which the air for combustion is pre-heated to a high temperature. It is obvious that the risk of the overheating of the grate is greatly increased, when air for combustion is used that has been preheated to a high temperature (for example to a temperature of 400 0.). This overheating, in the case of grates to which the invention relates, is liable to burn out or warp the fire-bars and consequently to cause jamming of the reciprocating members of the grate with the result that the grate ceases to function as a stoker. By the cooling of the grate. members in accordance with the present invention these drawbacks are overcome even when very highly heated air for combustion is used.

'In the operation of the grate the movable grate members are not moved vertically but solely longitudinally so that jamming, such as has heretofore been experienced with grates in which the movable grate members are moved vertically, is practically eliminated. In this section, while any suitable means may be employed to reciprocate the movable grate members without moving them vertically, one such means has been conventionally illustrated in the present instance as comprising a rock shaft 10 to be rocked in any suitable manner as, for example, by means of a handle 11, and having an arm 12 slotted at its free end as at 13 and engaged with a rod or pin 14 carried by one or more of the movable grate members. That is to say, the rod or pin 14 may be common to all of the movable grate members and there may be only a single arm 12 on the shaft 10 engaged with said rod or pin, or there may be an arm 12 and pin 14 individual to each movable grate member. In any event the arrangement is such that the movable grate members are not moved vertically but only reciprocally to advance the fuel. Moreover, it will be observed in this connection that the tops of all of the grate members are transversely flat and that while the'movable grate members may have teeth or projections z, the tops of all of the grate members may be said to be disposed substantially in a common plane so that the top of the grate at all times is practically flat. Thus, since the uppermost portions of the movable grate members are effectively cooled, any burning of such members is effectively avoided. At the same time, while the fuel may be effectively advanced, the bed of fuel remains advantageously of even depth throughout and is-not disrupted as in prior grate structures wherein the movable grate members are moved vertically.

What I claim is:--

1. In an'automatic furnace-grate, the combination of longitudinal grate members extending throughout the entire length of the grate and capable of reciprocation back and forth for feeding the fuel along the grate, and tubular members likewise extending throughout the entire length of the grate in close vicinity to said grate members and constructed for the circulation of a cooling medium to thereby indirectly cool said grate members, said tubular members having welded thereto flat plates disposed in substan-' tially the same plane with the surface of said grate members, air gaps being provided between said plates andsaid grate members.

2. A grate structure comprising a plurality of grate members disposed in side to side relation ship, all of said members having top surfaces which are substantially flat transversely, certain of said members being hollow for the circulation of a cooling medium therethrough, the remain-' ing members being solid and interspersed with respect to the hollow members, certain of said members being solely reciprocal to advance the fuel, and the tops of all the grate members being disposed at all times in substantially a common plane so that all portions of said solid members are at all times maintained cool by said hollow members.

3. A grate structure comprising a plurality of grate members disposed in side to side relationship, all of said members having top surfaces which are substantially flat transversely, alternate of said members being hollow for the circulation of a cooling medium therethrough and the remaining members being solid, certain of said members being solely reciprocal to advance the fuel, and the tops of all the grate members being disposed at all times in substantially a common plane so that all portions of said solid members are at all times maintained cool by said hollow members.

l. A grate structure comprising a plurality of grate members disposed in side to side relationship, certain of said members being solid and the remaining members being interspersed with respect to said solid members and being hollow for the circulation of a cooling medium therethrough, said hollow members being of substantially triangular shape in cross section and each having a substantially flat side thereof disposed uppermost, certain of said members being solely reciprocal to advance the fuel, and the tops of all the grate members being disposed at all times in substantially a common plane so that all portions of said solid members are at all times maintained cool by said hollow members.

5. A grate structure comprising a plurality oi grate members disposed in side to side relationship, certain of said members being solid and the remaining members being interspersed with respect to said hollow members and being in the form of tubes for the circulation of a cooling medium therethrough, said tubes being of circular cross section, substantially flat plates fastened to the tops of said tubes, certain of said members being solely reciprocal to advance the fuel, and the tops of all the grate members being disposed at all times in substantially a common plane so that all portions of said solid members are at all times maintained cool by said tubular members.

6. A grate structure comprising a plurality of grate members in side to side relationship, certain of said members being solid and the remaining members being interspersed with respect to said solid members and being hollow for the circulation of a cooling medium therethrough, said hollow members being of substantially rectangular shape in cross section and each having a substantially flat side thereof disposed uppermost, certain of said members being solely reciprocal to advance the fuel, and the tops of all the grate members being disposed at all times in substantially a common plane so that all portions of said solid members are at all times maintained cool by said hollow members.

7. A grate structure comprising a plurality of grate members disposed in side to side relationship, alternate of said members being in the form of tubes for the circulation of a cooling medium therethrough, said tubes being of circular cross section, means superimposed upon said tubes to provide grate surfaces which are substantially flat in cross section, the remaining members being solid and being solely reciprocal to advance the fuel, and the tops of all the grate members being disposed at all times in substantially a common plane so that all portions of said solid members are at all times maintained cool by said tubular members.

8. A grate structure comprising a plurality of grate members disposed in side to side relationship, alternate of said members being solid and solely reciprocal to advance the fuel, and the intermediate members being stationary and of hollow construction for the circulation of a cooling medium therethrough, all of said members having top surfaces which are substantially flat transversely, and the tops of all the grate members being disposed at all times in substantially a common plane so that all portions of said members are at all times maintained cool by said hollow members.

FERDINAND GRAAFEN. 

